Predicting Diamondbacks Starting Pitcher Success

Pretty often here on the internet we talk about non-elite pitchers as being more or less crap shoots. It’s true, pitchers tend to be more volatile than hitters, mostly because they get hurt more often. Luck can swing an ERA pretty wildly and trying to make bets on run-of-the-mill pitchers is just hard to do in confidence. What will Chase Anderson be like next year? Hell, I have no real idea. I can see a pretty good pitcher and I can see a guy who just doesn’t even make the rotation aside to fill in for an injury in June. That’s not really the position you want to be in with your hurlers and I think we’ve all seen enough of that in Arizona over the last couple of years.

One way that pitchers are like hitters is that they have feelings. Another way that pitchers are like hitters is that they are served well when they have a particular carrying tool. And I’ll be very liberal with “tool” here. Generally when we throw that term out it’s in regard to something mechanical – fastball velocity, command, the ability to hit for power, a strong throwing arm, etc. It’s pretty generally accepted that a hitter needs to have at least one very good to excellent tool to remain employed in the majors. Similarly, a pitcher needs to have one special ability to remain on the mound for any notable length of time. It can be an obscene number of grounders, extreme numbers of fly balls, massive strikeout totals, a minuscule walk rate, whatever. You have to have at least something going for you on the mound.

The above alludes to something you’ve probably read here at Inside the ‘Zona or heard Ryan and I discuss on The Pool Shot. Being in the middle as a pitcher just isn’t a good place to be, at least not from a consistency standpoint. Fly balls at Chase Field are problematic, but when a pitcher is able to rack up an excessive number of fly balls, he moves into a realm of effectiveness, even in a hitter’s park. Being a contact manager is tough, but it can be done effectively. Look no further than Brad Ziegler and soon-to-be-very-rich Darren O’Day. They have wildly different profiles: Ziegler leads the league in GB%, O’Day ranks near the top of the league in FB%. Neither is a flame thrower (although O’Day clearly has the edge on Ziegler) but they’re both effective by generating a certain kind of contact. This principle applies to starters, too, and that’s where we’ll direct our focus today.

Over at FanGraphs, Tony Blengino has been doing some very intriguing work with the batted-ball data that’s available thanks to StatCast. With his help, we’ve been able to see just how well certain pitcher tools (or traits) carry over from year to year. You can read more about that here, and I highly recommend it. For the sake of brevity, let’s just review which traits are stable, less stable and unstable from year-to-year (with correlations in parenthesis – the closer to 1 the more stable, the closer to 0 the less stable):

Stable

• K% (.81)
• BB% (.66)
• FB% (.76)
• GB% (.86)
• FIP (.65)
• SIERA* (.72)

Less Stable

• Pop Up% (.53)
• ERA (.45)

Unstable

• LD% (.14)

Hey look, that’s neat. There are definitely some tools and/or traits that we can feel pretty comfortable about. GB%, K%, FB% and others remain pretty consistent year in and year out, meaning we wouldn’t expect any big swings from one year to the next in those categories. Pop ups/infield fly balls are pretty stable, although not as stable as the others above. We know ERA has it’s issues and that’s why we use FIP and other ERA-estimators here the vast majority of the time. Line drive rate always has been and always will be wildly unpredictable.

*One note: Blengino uses his own personal metric called “tru” ERA, which incorporates batted ball data. This is what SIERA is designed to do, too, and although the two are surely different, I’ve inserted SIERA here to replace “tru” ERA since they’re similar and we know SIERA is the most stable ERA-estimator from year-to-year.

So with this knowledge going forward, we can put a handful of Diamondbacks starters under the microscope to see to what degree we think they may have similar or dissimilar seasons in 2016. Well, actually less than a handful since Jeremy Hellickson got traded recently. We’ll keep Rubby De La Rosa in here for now even though I’m convinced he’s a reliever. With 80 innings pitched as the cutoff, we’re left with Anderson, De La Rosa, Patrick Corbin and Robbie Ray. Here are their 2015 numbers, along with their percentile rank for each category out of 147 total pitchers.

 *click to enlarge

So let’s apply the previous discussion to these four pitchers. Only Rubby De La Rosa was a standout in the ground ball category, and we’d expect him to still get grounders going forward. Because of the volatility associated with line drives, we can more or less assess that Ray, Corbin and Anderson were unlucky and De La Rosa was lucky. For fly balls, Corbin didn’t give up very many, but the sample size of his innings give a little a pause. Ray and Corbin were both good for strikeouts; Anderson and De La Rosa were not. Corbin didn’t walk anyone (again, SSS warning) while Ray issued too many free passes, as did De La Rosa. If we synthesize this, we’d expect these four traits (GB%, FB%, K% and BB%) to translate pretty well to next year, which bodes well for some and not so well for others.

I left ERA and SIERA out of the previous discussion for a reason. These are the “end results” of a lot of the things above. ERA says what happened with all of those grounders, flies, strikeouts, walks and more. SIERA says what should have happened with all of those things. We can look at the ERA numbers and acknowledge that Ray and Corbin had nice seasons (when they were pitching) while Anderson and De La Rosa weren’t very good at all. But SIERA is both more accurate as an indicator of true talent and is more consistent from year-to-year than ERA. By that measure, Corbin really was very good, Ray was just okay and both Anderson and De La Rosa  were still nothing to write home about. We should feel relatively confident that those brief descriptors will carry forward. Lastly, to clarify, I didn’t include FIP because it fits between ERA and SIERA and really why make this any  more complicated than it needs to be?

Here’s what I take from this for each pitcher, for better or worse:

• Robbie Ray outperformed his peripherals a bit in 2015 and, unless he can get a breaking ball figured out and limit the walks, he won’t get any better than he is right now, which is truly more okay than good.
• Patrick Corbin was solid across the board, and even though his small sample distorts his numbers a little, his ability to strike guys out and not walk them makes him a potentially top 15 pitcher in baseball.
• Chase Anderson’s batted ball profile puts him in the danger zone and the drop in strikeouts really hurt him. He’s a rotation filler and nothing more at this point.
• Rubby De La Rosa got some ground balls and did nothing else well. The fact that he was in the 9th percentile for LD% and still had an ERA and SIERA that were poor says it all. If he can’t get out lefties (never has, probably never will), he’s a RP.

This is the snapshot we’re left with. It holds true at this place and time. That doesn’t mean it won’t change going forward, but armed with some new information, we know that we should expect certain things to hold steadier than others. The ground ball guys will be the ground ball guys, for example. The strikeouts will remain for Corbin, the walks for Ray. We might expect a decrease in line drives for Anderson, Ray and Corbin, and an uptick for De La Rosa.

There are, of course, pieces of this puzzle we cannot predict. Will Robbie Ray finally learn a functional breaking pitch? Will Rubby De La Rosa be moved to the bullpen or traded? Will Chase Anderson be traded or even make the Opening Day rotation? Can Patrick Corbin stay healthy? We can’t know these things for sure. But based on what the pitcher can control and has done in the past, we have a clearer picture moving forward. That picture supports the team’s need to address the rotation in the immediate future, trim the fat (or at least limit it) and not rely too heavily on Robbie Ray’s initial success. If they apply the right context, there’s no reason not to make the necessary changes.